The invention relates to an inlet structure of the covered or open type, with one or more semiaxial-throughflow or axial-throughflow pumps arranged therein, for use in power plants and/or in water conservation plants, an inlet nozzle of a pump being arranged in an inlet chamber so as to maintain ground clearance.
Such inlet structures are often used in pumping stations in which large quantities are to be conveyed. For example, in power plants or plants for the irrigation or drainage of large areas of land, such inlet structures must conform to specific conditions in order to meet the requirements placed on them. The problems of such inlet structures are described in detail in the article xe2x80x9cEinfluxcex2 von Kxc3xchlverfahren und Zulaufbedingungen auf die Bauart von Kxc3xchlwasserpumpen fur Warmekraftwerkexe2x80x9d [xe2x80x9cInfluence of cooling processes and inflow conditions on the design of cooling-water pumps for thermal power stationsxe2x80x9d] by A. Migod and H. Siekmann, KSB Technische Berichte [KSB Technical Reports], No. 17, 1977, pages 25 to 45.
U.S. Pat. No. 1,476,210 shows various designs of such inlet structures with pumps installed therein. It becomes clear from this that the structure costs assume great importance in the production of such stations. The costs of producing such a structure may easily exceed the actual costs of the pump.
DE-B-21 37 637 describes the hydraulic problems of inlet chambers necessarily installed in such structures. The installation of a baffle is intended to achieve an optimized inflow to the inlet nozzle of a pump. This is necessary, since, predominantly, a plurality of inlet chambers are arranged in an inlet structure. Depending on the switch-on states of the pumps and on the conditions of inflow to the inlet chambers, therefore, inflow conditions often arise which may have adverse effects on the suction behaviour.
The object of the invention is, for such inlet structures with a multiplicity of pump and inlet chambers, to achieve optimization of the structural measures, whilst at the same time improving the inflow conditions.
This problem is solved by the invention as described and claimed hereinafter.
Arranging the pump with its inlet nozzle and/or with part of its casing in the depression ensures that a first pump impeller adjacent to the inlet nozzle is arranged at a lowest point in the inlet structure. By the inlet nozzle being arranged in a depression of the floor surface of the inlet structure, the total outlay involved in constructing the latter can be decisively reduced. Excavation work and foundations for the inlet structure and the inlet chambers no longer need to have the depth which has been necessary hitherto. The same applies to inflow gutters or channels, by means of which a medium to be conveyed has been supplied to the pump. Instead, a lowest point for the structure is now provided only in the region of the inlet nozzle in a simple way at the place of installation of such a pump. Consequently, each inlet nozzle of such pumps penetrates, as it were, into a pit, the upper edge of which is at the same the lower edge of a basin or channel delivering the medium to be conveyed.
Arranging the pump inlet nozzle in such a depression affords the additional advantage of improved conditions of inflow to the first impeller of such a pump. The turbulences prevailing in conventional inlet structures on account of the multiplicity of channels, inlet chambers and branches are compensated by the directional inflow between the depression and the pump part located therein.
Since the medium to be conveyed is guided more effectively as a result of inflow between the wall surface of the depression or of the pit and the pump part located therein, the inflow conditions which present problems in the known inlet chambers are compensated.
Furthermore, pumps of smaller diameter with higher rotational speeds can be used. The higher NPSH necessary for this purpose is provided in the simplest possible way by the cost-effective production of the local depression, as a result of which the costs for the pump and drive and also the structure costs are ultimately reduced by a multiple.
In one embodiment of the invention, the pump is of the single-stage or multi-stage type. It is consequently possible in a simple way to adapt to the respective plants and their conveying conditions. The inflow cross section between the depression and the pump part, with the inlet nozzle, located therein and the length of the depression are dimensioned such that the pump can be operated without cavitation and, with a view to high efficiency, the losses are kept as low as possible.
Single-stage spiral-casing pumps with complicated concrete spirals are often used for drainage or irrigation purposes and large quantities of cooling water. This type has a significant height difference between the entry level and exit level, but is substantially more complicated to produce. The solution according to the invention achieves the significant advantage that a metallic pump, for example a tubular-casing pump or a submersible motor-driven pump with delivery duct can be used in the same field as spiral-casing pumps in the simplest possible way with very low costs in terms of construction. As a result of the simple depression, into which the suction nozzle of a first impeller is lowered, the remaining structure depth of the inlet structure can be substantially smaller. Consequently, there can be considerable saving in terms of excavation work, securing and supporting work and also concreting costs.
An additional advantage is afforded by the different design of such structures which becomes possible as a result. The spacious inlet and inflow structures which have been necessary hitherto, and also the long inflow or connecting channels having a slight descending gradient can likewise be reduced with regard to their construction volume. It is sufficient, in the respective place where a medium to be conveyed occurs, to provide the arrangement of a correspondingly low suction point for the pump, in order to convey said medium to respective intended location again with the aid of simple delivery lines.
Further embodiments of the invention provide a streamlined transition at the transition between the inlet chamber and the orifice of the depression. This avoids unfavourable vortices being generated in the event of a deflection of the flow. Also, depending on the length of the pump, the latter may be arranged in the depression so as to be freely suspended or with supporting elements being interposed. This depends on the respective installation situation and on the plant conditions.
Also, within the depression, one or more flow-guiding guide elements are arranged, with the aid of which the cavitation behaviour is influenced.
According to other refinements of the invention, the depression consists of completely or partially prefabricated structural parts. These may be finished concrete parts or prefabricated commercially available structural parts which can be used for such purposes.